1. Field of the Invention
The present invention relates to a master information carrier which is used when an information signal such as of preformat information is initially recorded to an information recording medium and also which has such a region, on the surface of a base member, in which a pattern corresponding to such an information signal is formed that is higher in level than the other regions. More particularly, the present invention relates to a technology for eliminating such damages and improper uniform adhesion of the information medium due to sticking/residing of foreign matter at the time of transfer-wise recording of the information signal to the information recording medium.
2. Description of the Related Art
A master information carrier is used to transfer and record a preformat information signal to a magnetic recording medium. The preformat information signals include a tracking servo signal, an address information signal, a reproduction clock signal and the like. Such a signal is recorded at a constant angle pitch in each track of a disk which is the magnetic recording medium. In the master information carrier, a shape pattern made of a ferromagnetic thin film corresponding to an information signal on the surface of the base member is formed. The master information carrier is adhered to the magnetic recording medium to transfer and record the shape pattern corresponding to the information signal in the master information carrier on the magnetic recording medium as an information signal by an action of magnetization.
To make sure of adhesion, the base member of the master information carrier is sectioned into a high-level region and a low-level region by means of a step so that the shape pattern corresponding to the information signal is formed in the high-level region.
If some foreign matter exists in a high-level region of the master information carrier, uniform adhesion cannot be secured between the high-level region and the magnetic recording medium. Then, the master information carrier is washed. After being washed with a detergent such as pure water or an organic solvent, spin-drying is carried out by means of rotating the master information carrier at a high speed to remove the detergent by centrifugal force.
In such spin-drying, there is observed such a phenomenon that flow of the detergent becomes stagnant at an edge of the high-level region so that minute foreign matter contained in the detergent may stick to the edge. This phenomenon causes a problem if the foreign matter sticks to and resides on the surface of the high-level after washing.
If foreign matter thus sticks and resides, it is impossible to uniformly adhere the high-level region and the magnetic recording medium with each other, thus possibly damaging the surface of the magnetic recording medium or the surface of the high-level region in the master information carrier at adhering.
Therefore, a transferring and recording method of adhering the magnetic recording medium and the high-level region in which a ferromagnetic thin film pattern is formed in the master information carrier has an important subject of preventing detergent or foreign matter from stagnating at an edge of the high-level region during a detergent drying step for the master information carrier, for the purpose of improving the adhesion thereof.
Such a subject applies not only to a magnetic recording medium for magnetically recording/reproducing but also to an information recording medium of any other recording/reproducing types.
Accordingly, a main object of the present invention is to provide a high-reliability master information carrier which can uniformly adhere a high-level region and an information recording medium without damaging the information recording medium when an information signal such as a preformat information is transfer-wise recorded to the information recording medium such as a magnetic recording medium in a master information carrier.
Another object of the present invention is to provide a method for manufacturing a high-reliability information recording medium.
The invention about the master information carrier solves the above-mentioned problems by taking the following measures. The invention premises a structure of a master information carrier in which a region having a shape pattern corresponding to an information signal on the surface of a base member is provided as a high-level region higher than the other regions. In the master information carrier having this premised structure, a required area of a rising edge which defines the high-level region has such a shape that protrudes externally so as to promote flow of a detergent, e.g., a curved shape which protrude externally convex shape or a polygonal shape consisting of a plurality of straight lines so as to protrude externally convex shape. Such a shape is called a flow promoting shape.
Here, a high-level region on the base member surface refers to a relatively higher region in which an information signal is formed with respect to a relatively lower region (which is called a low-level region) in which an information signal is not formed. Further, the rising edge which defines the high-level region refers to a portion having a step which forms a boundary between the high-level and low-level regions on the base member surface. Further, the required area of the edge refers to an area where a detergent or foreign matter contained therein is liable to stagnate during a drying step after washing.
In short, the master information carrier of the present invention includes a base member, a high-level and low-level regions which are constituted with a step formed therebetween on the surface of the base member, a shape pattern corresponding to an information signal formed on the surface of the high-level region, and a flow promoting portion which is formed in a required area of an edge at a boundary defining the high-level and low-level regions and has a shaped protruding externally so as to promote the flow of a detergent.
The structure of the present invention has the following actions. The area where a detergent or foreign matter is liable to stagnate is the edge of the high-level region which extends perpendicularly or nearly perpendicularly with respect to the flow direction of the detergent. At such an area, smooth flow of the detergent tends to be blocked. Even if the flow of the detergent hits the edge, it is stopped and stagnates there and once it stagnates, the following detergent flow is stopped by this stagnant detergent and may not reach the edge. Then, the stagnated state becomes permanent. This means, in short, stagnation (see detergent-flow stagnating region 54 shown in FIG. 22).
The above-mentioned stagnation is caused, as mentioned above, by a fact that the edge of the high-level region extends perpendicularly or nearly perpendicularly to a flow direction of a detergent. Then, in accordance with the present invention, a required area where a detergent or foreign matter contained therein is liable to stagnate is shaped as the flow promoting portion to protrude externally, i.e. opposite the flow of the detergent so as to promote the flow of the detergent without blocking it. By this protruding shape of the flow promoting portion, the flow of the detergent is promoted.
By such a countermeasure, it is possible to smooth the flow of a detergent at an area (position) where it is liable to be blocked, thereby preventing the detergent from stagnating therein. The detergent can thus be prevented from stagnating and therefore foreign matter contained therein can be prevented from being stagnated.
Here, a master information carrier in accordance with the present invention is reconfirmed as follows. The master information carrier is something like, so called an original text for initially recording an information signal of, e.g., preformat information on an information recording medium and has such a pattern (which is represented by a ferromagnetic thin film pattern) formed therein that corresponds to an information signal such as preformat information. An aspect of the information signal recording from the master information carrier to the information recording medium is transfer-wise. That is, the surface of the master information carrier is contacted with the surface of the information recording medium, thereby recording the information signal to the information recording medium transfer-wise by means of required processing (magnetization of a ferromagnetic thin film pattern in the case of a magnetic recording medium). Most important thing in such transfer-wise recording is to uniformly adhere the master information carrier to the information recording medium. It is important to uniformly contact the master information carrier to the information recording medium at least one region of this carrier in which region the above-mentioned pattern is formed not in the other regions where the pattern is not present. One technique to further effectuate this uniform adhesion is to raise in level the region where the pattern is formed higher than the other regions where the pattern is not formed. That is, the surface of the master information carrier is sectioned into a high-level region and a low-level region so that the pattern is formed in the high-level region. The high-level region has a high possibility than the low-level region of adhering the surface of the information recording medium. The low-level region needs not be adhered since it does not have the pattern formed therein. Such partial adhesion in the high-level region not throughout adhesion enables highly uniform adhesion.
By sectioning the surface of the master information carrier into the high-level and low-level regions, another advantage can be obtained. In a state where the master information carrier is in contact with the information recording medium, there is provided a gap in the low-level region, which gap can be used as a degassing path. Although there is air in the degassing path, by degassing through the path, the low-level region has a negative pressure so that negative-pressure suction may enhance the adhesion between the high-level region and the information recording medium.
No matter whether there is a level difference between the high-level and low-level regions on the surface of a master information carrier, that is, even if the master information carrier is flat throughout on its surface, foreign matter, if any on the surface, may damage the surface of the information recording medium when the master information carrier is contacted with it. Then, it is important to surely remove foreign matter which may possibly be on the surface of the master information carrier beforehand. The foreign matter may typically be removed by washing the master information carrier using a detergent such as pure water or an organic solvent. After washing, it is dried.
At a time of washing and drying the master information carrier, there is involved a problem of an irregularity between the high-level and low-level regions on the surface thereof. Although the section between the high-level and low-level regions forming the irregularity is, as mentioned above, effective in improving the uniform adhesion of the master information carrier to the information recording medium, this irregularity caused by thus sectioned high-level and low-level regions presents a problem in washing and drying for removing of the foreign matter. That is, a step boundary between the high-level and low-level regions, i.e. an edge acts as a weir that blocks the flow of a detergent.
At the edge thus acting as a weir, the detergent is liable to stagnate, and foreign matter contained therein is also liable to stagnate. After drying, the foreign matter remains as stuck there. Most of the foreign matter is removed for sure since the carrier is washed. However, a meager part of foreign matter resides as stuck there. This foreign matter stuck and residing on the master information carrier, even if only a little, may damage the surface of the information recording medium when the master information carrier is adhered with it, causing a significant problem. There is also another significant problem that the stuck and residing foreign matter may deteriorate the uniform adhesion of the master information carrier to the information recording medium.
The present invention has had such a background. As mentioned above, in accordance with the present invention, a required area where a detergent or foreign matter contained therein is liable to stagnate would protrude externally in a curved or polygonal convex shape so as not to block the flow of the detergent toward the area, i.e. such a flow promoting shape that inflates toward the outside. Such a shape serves to smooth the flow of the detergent and prevents the detergent and also foreign matter contained therein from stagnating at the area. Therefore, it is possible to eliminate the sticking and residing of foreign matter also at the edge, which is the boundary between the high-level and low-level regions, thereby realizing high-level cleaning throughout on the surfaces of the master information carrier.
As a result, in a master information carrier of such a structure that a high-level region is supposed to have such a pattern (which is represented by a ferromagnetic thin film pattern) formed therein that corresponds to an information signal and also that partial tight contact caused by an irregular shape of that region is combined with negative-pressure suction due to degassing thereof to enhance uniform adhesion with an information recording medium in order to transfer and record the information signal from the high-level region to the information recording medium, the present invention enables completely removing foreign matter, thereby effectuating the uniform adhesion truly. Moreover, it is made possible simply by controlling the required area into an inflated curved or polygonal shape eliminating complicated and expensive devices, thereby giving a great advantage.
The curved shape of the inner radial edge of the high-level region may be any one of an arc, part of an ellipse, a parabola, a hyperbola, any other quadratic curve, and any combination thereof. The polygonal shape may also be any one of a wedge and any polygon consisting of a plurality of straight lines externally protruding convex shape as far as the number of these lines is two or larger and no matter whether an angle between any two adjacent ones of these lines may be an acute, right, or obtuse angle.
Preferred aspects of a master information carrier of the present invention will be comprehensively described below.
In the above description, the preferred aspect may have the flow promoting shape formed at an inner radial edge near the center of the base member.
Here, the master information carrier and the information recording medium are assumed to be disk shape. In the disk-shaped information recording medium, a pattern which corresponds to an information signal such as of preformat information is formed in a region taken along in an approximately radial direction of the disk. For the purpose of drying a detergent, spin-drying is mainly employed by use of a centrifugal force. At this time, the detergent or foreign matter contained therein is liable to stagnate at the inner radial edge of the high-level region since the edge has a relatively small centrifugal force (F=rxcfx892), which is proportional to the radius. Then, the inner radial edge of the high-level region is transformed into a flow promoting shape, thereby inhibiting possible stagnation to smooth the flow of the detergent, and preventing the detergent and foreign matter contained therein from sticking and residing.
Further, in the above description, the preferred aspect is that the curved shape according to the flow promoting shape portion has a arc shape. The arc shape relatively simple shape and easy to form, so that the present invention is advantageous in development.
In the above description, the preferred aspect is that the polygonal shape according to the flow promoting shape portion has a wedge shape. The wedge shape is relatively simple shape and easy to form and excellent in smoothing the flow of the detergent, so that the present invention is advantageous in development.
In any case of the curved and polygonal shapes, the preferred aspect is that the base member is made of a nonmagnetic material and the pattern formed in the high-level region is a thin film pattern made of a ferromagnetic material. This permits not only a flexible disk but also a hard disk to properly record thereon an information signal such as of preformat information transfer-wise.
In addition, in the above description, the preferred aspect is that the base member has a disk shape and a plurality of the high-level regions is formed in a state approximately taken along in a radial direction of the disk-shaped base member with the low-level region being inserted between each two regions thereof which are adjacent to each other in a circumferential direction.
In the disk-shaped information recording medium, in units of a sector obtained by subdividing the disk at a predetermined angle pitch, preformat information signals such as a tracking servo signal, an address information signal, and a reproduction clock signal are previously recorded in the circumferential direction. There is the information recording medium having a form in which those preformat information signals are arranged in an approximately radial direction (in a radius direction). This structure corresponds to that of a recording/reproducing head moves in the radius direction of the information recording medium. When the head actuator is of a rotary type like a magnetic disk, the recording/reproducing head traces an arc-like approximately taken along in the radial direction of the information recording medium. If the head actuator is of a direct-acting type like a mini-disk (MD), on the other hand, the recording/reproducing head traces a straight line approximately taken along in the radial direction of the information recording medium.
Corresponding to such an array of the preformat information signals in the information recording medium, the information signal patterns are also arrayed radially on a master information carrier. In accordance with the present invention, the information signal patterns are formed on the high-level region while a plurality of the high-level regions are radially formed. Between each two of these high-level regions which are adjacent to each other circumferentially, a low-level region is inserted. As a result, the low-level regions are also arrayed radially.
In the plurality of high-level regions thus arrayed radially, the respective inner radial edge protrudes externally in a curved shape or in a convex shape of a polygon consisting of a plurality of straight lines. That is, the edge is shaped so as to promote the flow.
Since the inner radial edge is thus shaped into the flow promoting portion, when the disk-shaped master information carrier is washed, as mentioned above, it is possible to smooth the flow of a detergent used to prevent the detergent and foreign matter contained therein from stagnating at the edge, thereby realizing sophisticated and clean washing. Also, each of the plurality of high-level regions is radially elongated and has a low-level region on both sides thereof, thus enabling highly adhesion of the high-level region, in which the information signal pattern is formed, of the master information carrier to the information recording medium. Further, each of the radial low-level region interconnects the center of the disk-shaped base member and the outer periphery, so that uniform adhesion can be improved between the information recording medium and the master information carrier by means of a negative pressure brought about by vacuum-sucking the low-level region through the degassing path.
By a synergetic effect of those three actions (partial adhesion, negative-pressure suction, flow promoting shape), it is possible to high accurately record an information signal pattern transfer-wise to an information recording medium at a disk-shaped master information carrier, i.e. a high-level region.
The present invention also relates to a method for manufacturing the information recording medium.
The manufacturing method of the information recording medium according to the present invention manufactures the information recording medium by using the master information carrier having any aspects described above. That is, first a step is performed for superposing any one of the above-mentioned master information carriers which has an information signal pattern formed on the surface of a high-level region of a base member and also which has a flow promoting shape at a required area of an edge of the high-level region onto an information recording medium with the information signal pattern as adhered and then another step is performed for transferring and recording the information signal pattern on the master information carrier onto the information recording medium as an information signal.
Here, it is assumed that the information recording medium may be a magnetic recording medium such as a hard disk, a magneto-optical recording medium such as a mini-disk (MD), or an optical recording medium such as a DVD (Digital Versatile Disk).
In the case of manufacturing the information recording medium using a master information carrier having a flow promoting shape at a high-level region in which the information signal pattern is formed, the master information carrier is already cleared of foreign matter substantially completely and highly clean and the high-level region is also partially adhered and the low-level region is degassed, so that it is possible to transfer and record the information signal pattern at a high accuracy and also to manufacture the information recording medium free of foreign matter.
In the above description, if the information recording medium is a magnetic recording medium, the following aspect may be preferable. That is, the base member is nonmagnetic and an information signal pattern formed in a high-level region of the nonmagnetic base member uses the master information carrier constituted of the shape pattern of a ferromagnetic thin film. Further, such a magnetic recording medium may be used that a magnetic recording layer made of a ferromagnetic thin film is formed on the surface of the nonmagnetic base member.
Then, in the case that the master information carrier is superposed on the magnetic recording medium in an adhesion state and the information signal pattern on the master information carrier is magnetically transferred and recorded on the information recording medium, a ferromagnetic thin film corresponding to the information signal pattern is magnetized by applying an external magnetic field, so that the information signal pattern is transferred and recorded as a magnetized pattern on a magnetic recording layer of the magnetic recording medium by a leakage flux from the ferromagnetic thin film.
Alternatively, prior to the superposition of the adhesion state, a first external magnetic field is applied on said information recording medium to initially magnetize said magnetic recording layer of said information recording medium and subsequently at time of said adhesive superposition, a second external magnetic field having a polarity opposite to that of said first external magnetic field is applied to transfer and record said information signal pattern as a magnetization pattern onto said magnetic recording layer of said magnetic recording medium.
As mentioned above, in the case that the magnetic recording medium is manufactured by using the master information carrier having the flow promoting shape on the high-level region in which the information signal pattern is formed, since the master information signal pattern is highly cleaned by substantially and fully removing the foreign matter, and the high-level region is partially contacted tightly and the low-level region is degassed, so that the transferring and recording of the information signal pattern is performed at a high accuracy and the magnetic recording medium without adhering the foreign matter can be manufactured.